Satellite Positioning System antennas and receivers, such as those for the Global Positioning System (GPS) and for the Global Navigation Satellite System (GLONASS) discussed below, are now used for many applications requiring determination of the observer's location anywhere on or in the vicinity of the Earth.
A differential GPS (DGPS) receiver includes a GPS antenna to receive the GPS signals transmitted from one or more GPS satellites, a GPS processor to calculate the GPS antenna's position mid time of observation of that position from the GPS signals, a display processor to convert the GPS position and observation time into information that is useful for an application, and a display to present the information to the user, and a DGPS antenna and processor to receive and apply differential corrections to produce GPS signals with improved accuracy. The GPS antenna must be positioned with a direct line of sight to the GPS satellite or satellites from which the receiver receives GPS signals.
Typically, GPS devices used in DGPS applications require numerous separate, distinct component units which are connected via cables. For example, the GPS receiver and processor would constitute one unit and the terrestrial radio would constitute a second unit, which would be coupled to the GPS processor via a cable. Typically, an input/output (I/O) unit which includes a display for data monitoring and a keypad for data input is also required. The I/O unit is coupled to the GPS receiver/processor unit and to the terrestrial radio via cable. Some systems also require the attachment of a separate battery via cable. Because multiple separate units are used in these prior art systems, the systems are bulky and difficult to move around.
For example, one type of GPS receiver, generally referred to as “handheld,” includes a GPS antenna, a GPS processor, a display processor, and a display in a single unit. Another type of GPS receiver system places the GPS antenna in an antenna unit and the display in a separate display unit. The GPS processor and the display processor may be contained in the GPS antenna unit, the display unit, or in a separate unit. In both of these GPS receiver systems, the DGPS radio antenna and receiver are provided in a separate unit or units, which are connected to the GPS processor. The handheld format allows the user to separate the GPS antenna and the display units so that the GPS position and time information can be observed and operated upon in a protected environment.
However, using cables and connectors to couple multiple units of the DGPS systems often creates problems related to reliability and durability. This is particularly true for DGPS systems which are mobile because of the jarring and shaking of the system from use and movement. Additionally, the systems are expensive to manufacture and assemble. Furthermore, the connections are often bulky, expensive and prone to breakage or malfunction. In addition, it is difficult to move the various boxes and cables around.
Furthermore, typical GPS unit receivers are separated by long distances or by immobile structures. Therefore, radio relay units are used to get the signal from one GPS unit to anther GPS unit. Previous radio relay systems for relaying GPS signals typically include multiple separate components such as a transceiver operating at one frequency which is coupled via cable to a separate transceiver operating at a second frequency. These relay systems receive signals through an antenna which is connected to a processor by a cable, which is then connected to a radio by a cable, which rebroadcasts the signal through an antenna attached by cable to the radio.
These relay systems are bulky and difficult to move around. Furthermore, these relay systems typically are expensive and are difficult to maintain and operate due to the fact that each of the components of the radio relay system is unique. Additionally, most of the currently available systems are not durable and reliable enough for applications that require portability, such as surveying.
Therefore, a Differential Global Positioning System (DGPS) apparatus, contained in a single antenna-like package is desired. This will allow the user to place a GPS antenna in a direct line of sight from one or more GPS satellites, to operate and observe the position and/or observation time display in-a protected environment; and receive and process differential GPS radiowave signals to determine the corrected location and/or observation time for the device using GPS methods. Such a system would have portability, durability, reliability, and be inexpensive to manufacture and assemble.